Local transmural electrical stimulation by chronically implanted electrodes of a carotid artery in rabbits was daily repeated. The area in direct contact to the electrodes covered 0.5 x 5 mm of adventitia. The carotid walls received DC impulses (10 ms/imp, 10 Hz, 100 microA) 2 x 1/2 h daily. Within 4 weeks a proliferate of smooth muscle cells develops in the intima at the spot where the anode contacts the outside of the artery. If the animals were fed 2% cholesterol in normal food the proliferate developed to a typical atheroma. The other parts of the arterial system did not develop plaques within this time. At the luminal side of the plaques no significant adhesions of platelets could be seen. Addition of 300 mg 2-ethyl-3-[-4-hydroxybenzoyl]-benzofuran (benzarone, Fragivix) to 100 g of animal food (containing 2% cholesterol) caused a less pronounced increase of serum cholesterol than in the controls which received cholesterol-containing food without benzarone. The development of plaques could not be prevented by benzarone, however, the growth of the atheromatous plaque was inhibited and the incorporation of lipids into the plaques was less pronounced than in those animals which received a diet with cholesterol but without benzarone. In those animals which received benzarone more lipid-laden foam cells were seen moving through the endothelium out of the plaque into the lumen of the stimulated artery. These foam cells were of mononuclear origin.